NTSB Factual Report

On March 5, 2010, about 1630 central standard time, a single-engine, Beech A36 airplane, N2036Y, was substantially damaged during a forced landing following a total loss of engine power while in cruise fight near Slaton, Texas. The private pilot, the sole occupant, sustained minor injuries. The airplane was registered to and operated by the pilot. Visual meteorological conditions prevailed and a flight plan was filed for the 14 Code of Federal Regulations Part 91 personal flight. The 256 mile cross-country flight departed the Lubbock Preston Smith International Airport (LBB), Lubbock, Texas, about 1620 with the Dallas Executive Airport (RBD), Dallas, Texas, as the intended destination.

According to the pilot, while at 5,500 feet, he heard a “loud explosion” and the left front engine cowling blew open. Shortly thereafter, oil appeared on the windscreen and the engine stopped producing power. The pilot executed a forced landing to a flat plowed field. The airplane’s left wing separated at impact and the airplane came to rest in a nose down, but upright position. The pilot was able to exit the airplane unassisted.

The Federal Aviation Administration (FAA) inspector who responded to the accident site reported, that the engine’s #2 cylinder was found separated from the engine crankcase.

The engine, a Teledyne Continental Motors (TCM), IO-550-B-12B, serial number 271728-R, was examined at TCM in Mobile, Alabama. Oversight was provided by the NTSB investigator-in-charge (IIC). The examination revealed that all crankcase main bearing surfaces, except for #5, exhibited fretting wear. In addition, the crankcase cylinder decks exhibited wear patterns consistent with movement between all cylinders and the crankcase.

Additionally, the crankcase exhibited signatures consistent with the #2 cylinder rocking back and forth before it exited the engine case. The #2 piston to crankshaft connecting rod cap was found separated from the connecting rod. The #2 piston pin had been pulled through the lower section of piston, suggesting that the connecting rod to crankshaft separation was a secondary failure.

A review of the engine logbook revealed that the engine was overhauled on March 29, 2002. At the time of the accident, the engine had accumulated approximately 1,072 hours since major overhaul and 641 hours since a top overhaul.

On May 29, 1992, TCM issued Service Bulletin (SB) M92-9, which was applicable to all Continental 470’s, 520’s, and 550’s. This SB instructed that “at overhaul or when necessary … a 12 point nut must be used … and torqued to 790 – 810 inch lbs.” The accident engine was equipped with the earlier 6 point nuts which had a required torque of 690 – 710 in lbs. This nut is used on the crankcase through bolts and to secure the cylinders to the crankcase. It was also noted that the SB was not mandatory since the airplane was being operated under 14 Code of Federal Regulations Part 91.

NTSB Probable Cause

The loss of engine power due to the insufficient clamping force between the two crankcase halves and each cylinder to the crankcase.